An electric double layer capacitor is characterized in that electric energy is stored by physically adsorbing an anion and a cation present in an electrolyte on a positive polarity surface and a negative polarity surface of a polarizable electrode.
FIG. 2 shows an example of a conventional bipolar layered type electric double layer capacitor. As shown in FIG. 2, the conventional bipolar layered type electric double layer capacitor (hereinafter referred to merely as a capacitor) is a layered type capacitor in which an ion-permeable separator 103, and a polarizable electrode including flat activated carbon electrode plates 100 that are bonded onto opposite surfaces of a polarization substrate 102 are alternately layered.
In the following, there is explained the capacitor in which a cell 104 as a minimum unit is constituted of the separator 103 and the activated carbon electrode plates 100, 100 disposed on opposite surfaces of the separator 103. The capacitor includes a multi-layered type body formed by a plurality of cells 104 which are stacked on one another through the polarization substrate 102. The multi-layered type body is tightened by and between two end plates 107, 107 that serve as lamination-retaining metal plates. Packing members 105 are respectively disposed on opposite surfaces of an outer peripheral portion of the polarization substrate 102. The packing members 105 serve to separate the adjacent cells 104 from each other in a hermetically sealed manner for the purpose of preventing the electrolyte in the capacitor unit from leaking out of the capacitor unit. With the provision of the packing members 105, the polarization substrate 102 is sandwiched at the outer peripheral portion between the packing members 105. The packing members 105 also serve to insulate the adjacent cells 104 from each other.
Upon assembling the capacitor, the cells 104 that have necessary withstand voltage (for instance, about 2.5V per unit cell) are stacked together with the packing members 105. Finally, the stacked cells 104 and packing members 105 are fastened with the two end plates 107, 107 through two current collector electrode plates 106, 106 that serve as current collector metal end plates, respectively. Thus, the adjacent cells 104 are kept separated from each other in the hermetically sealed state. Current collector terminals 108, 108 are connected to the current collector electrode plates 106, 106, respectively.
In order to completely separate the adjacent cells 104 from each other in a hermetically sealed manner, it is necessary to apply a sufficiently large fastening force to the end plates 107, 107. For this purpose, the end plates 107, 107 are formed with screw holes, respectively, and the packing members 105 are formed with through-holes in a position where the through-holes are opposed to the screw holes, respectively. Metal screws 109 are inserted and screwed into the screw holes and the through-holes to fasten the end plates 107, 107 to each other (see Patent Document 1). More specifically, a female-threaded resin spacer (hereinafter referred to merely as a resin spacer) 113 is inserted into the respective through-holes of the packing members 105. The resin spacer 113 is a tubular member or a hollow cylindrical member which is made of a resin. The resin spacer 113 has a female-thread on an inner circumferential surface of opposite end portions thereof. The metal screws 109 are screwed into the opposite end portions of the resin spacer 113 to thereby fasten the end plates 107, 107 disposed on the opposite sides and produce a large pressing force that is applied to the stacked cells 104, the packing members 105 and the current collector electrode plates 106.
In view of the construction of the capacitor, there might occur potential difference between the end plates 107, 107. In the capacitor as shown in FIG. 2, since the end plates 107, 107 are in contact with the current collector electrode plates 106, 106, it is necessary to insulate one of the end plates 107, 107 from the other. For this reason, the resin spacer 113 are used as described. For example, polyphenylene sulfide (PPS) containing filler-like glass fiber may be used as a resin material for the resin spacer 113 from the viewpoint of strength, heat resistance and durability.
In addition, there has been conventionally proposed a capacitor in which a plurality of stacked cells are connected with one another in series. Each of the cells have a first terminal and a second terminal, and the first terminal of one cell is connected with the second terminal of the adjacent cell through a rectangular plate-shaped terminal connecting portion. The first terminal or the second terminal, and the terminal connecting portion are fastened to each other by means of bolts and nuts. The terminals, the terminal connecting portion and an insulating block that is disposed between the adjacent terminals are formed with through-holes, respectively. Hollow cylindrical sleeves made of an insulating material are fitted into the through-holes, and the bolts are inserted into the sleeves (see Patent Document 2).    Patent Literature 1: Japanese Patent Application First Publication No. 2003-217986    Patent Literature 2: Japanese Patent Application First Publication No. 2006-294985